The syntax for border-image is currently
<image>
[ <number> | <percentage>]{1,4} [ / <border-width>{1,4} ]?
[ stretch | repeat | round ]{0,2}
which is unusually restrictive for CSS. Normally we allow swapping
the order of various elements of a complex syntax. In this case,
I'd expect to be allowed to place the stretch/repeat/round keywords
before the URL as well as at the end.
I propose
[ <image> [ <number> | <percentage>]{1,4}
[ / <border-width>{1,4} ]? ]
&& [ stretch | repeat | round ]{0,2}
~fantasai